In carrying out strongly exothermic catalytically promoted reactions, a major problem arises in the control of the heat realized by the reactions. It has been found, for example in the methanization of carbon oxides, i.e. the reaction of carbon oxides with hydrogen in accordance with the relationships, EQU CO+3H.sub.2 .revreaction.CH.sub.4 +H.sub.2 O+Q EQU CO.sub.2 +4H.sub.2 .revreaction.CH.sub.4 +2H.sub.2 O+Q
that the evolution of the reaction heat Q is so great that especially severe problems arise, particularly in the case of high carbon monoxide concentrations, with respect to control of the reaction.
To avoid such difficulties, it has been proposed in German printed application (Auslegeschrift) DT-AS 12 71 301, to carry out the methane-production reaction in a step-wise manner in a plurality of successive (cascaded) adiabatically operated reactors. The capital costs of such installations are, however, very high, especially since the initial reactors must be provided with expensive linings or from refractory materials of high cost in order to withstand the high temperatures which must be sustained by the reactors.
German open application (Offenlegungsschrift) DT-OS 23 35 659 (corresponding to U.S. Pat. No. 3,958,956) discloses the production of methane-rich gases in isothermically operated reactors. Since lower temperatures prevail in isothermically operated reactors than in adiabatically operated reactors, the problems mentioned previously can be at least partly eliminated. However, in the latter process, it is found to be necessary to add to the reactants before they enter the isothermically operated reactor, a significant quantity of water vapor or steam. A disadvantage of this process is that the methanization reaction can only be carried out opitmally when the water is mixed with its reactants in special gas/liquid mass-exchange or contact systems. It is especially important to introduce superheated steam so that the threshold temperature necessary to trigger the exothermic reaction can be developed within the reactor.
The isothermically operated reaction system is also characterized by the significant technological disadvantage that precise control of the strongly exothermic reaction can only be effected by relatively complex and expensive process-control instruments and equipment. The control of the reaction is particularly difficult when the rate at which the feed stock is supplied to the reactor varies over a significant range.